Horizontal pressure casting machines (e.g., die casting and squeeze casting machines), include a die having a cavity therein for receiving and shaping molten metal and a shot sleeve for injecting the molten metal into the cavity. The shot sleeve is essentially a cylinder having a piston at one end and an opening at the other end communicating with the die cavity. Molten metal is poured into the cylinder via a filler hole in the cylinder wall located between the piston and the opening to the die cavity. To cast the metal, the piston advances pass the filler hole, causes the molten metal to fill the cross section of the cylinder, and pushes the molten metal, under pressure, into the die cavity.
In horizontal pressure casting machines the longitudinal axis of the shot sleeve is horizontal, and the shot sleeve is only filled up about half way with molten metal. As a result, the lower half of the shot sleeve is subjected to significantly higher temperatures than the upper half. This thermal differential can cause the shot sleeve to distort, or warp, unless the heat in the lower half can somehow be rapidly dissipated and spread more evenly over the entire shot sleeve. To this end, it is known to make a multilayered shot sleeve including an inner layer comprising a highly thermally conductive material, such as copper-beryllium alloy, to dissipate the heat build up (e.g., see Zecman U.S. Pat. No. 4,926,926). Zecman welds a copper tube about a steel liner and then shrink fits another steel tube about the copper tube. Shrink fitting of the outer tube leaves the inner barrel in compression and traps the copper tube between the outer tube and inner barrel.
The inside surface of shot sleeves are also susceptible to wear resulting from the piston's reciprocating back and forth therein, and to erosion by metals such as aluminum. To reduce the effects of wear and erosion in shot sleeves, it is known to line the inside surface of shot sleeves for vertical pressure casting machines with a cermet material. One known such shot sleeve comprises an H-13 steel tube having a TiC-Ti cermet material sintered in situ between a mandrel and the H-13 tube to form a liner for the tube. No bond is formed between the liner and the tube, and gaps of as much as 1/2 mm therebetween exist.
Shot sleeves made using the aforesaid techniques have some deficiencies. For example, in the cermet lined sleeve air gaps between the cermet lining and the H-13 steel tube cause nonuniform heat transfer therebetween. This condition is worsened at higher temperatures as the steel tube expands away from the cermet lining. Similarly in multilayered shot sleeves containing a highly thermally conductive, but unbonded, layer, air gaps can form between the several unbonded layers which reduce the effectiveness of the conductive layer in adequately dissipating the heat. For example, Zecman welds a copper tube to the exterior of an inner steel barrel, and then shrink fits an outer shell over the copper tube. Such layers are not bonded to each other and can have thermally resistant interfaces between the several layers. Another multi-layer design contemplates an inner H-13 steel tube surrounded by a copper tube which, in turn, is sheathed in an H-13 steel outer sleeve. The several layers are closely machined, and then simply pressed together with no bonding between the layers. Such assembly techniques do not provide the most effective uniform interfacial contact between the copper and the steel tubes that sandwich it and result in less effective thermal conduction between the layers then might otherwise be possible if a more intimate interface between the copper and the inner/outer tubes had been achieved.
The present invention contemplates a long-lived, multi-layered shot sleeve comprising a highly thermally conductive material and an erosion/wear resistant material interatomically bonded to each other for excellent heat transfer between the materials.